Fexofenadine polymorphs and processes of preparing the same

ABSTRACT

Anhydrous crystalline fexofenadine hydrochloride Form C, crystalline fexofenadine acetate monohydrate Form D, crystalline fexofenadine acetate dihydrate Form E and crystalline fexofenadine free base monohydrate Form F, processes of preparing the same, pharmaceutical compositions thereof, therapeutic uses thereof and methods of treatment therewith.

The present invention is concerned with fexofenadine polymorphs, processes of preparing the same and the use thereof in pharmaceutical formulations and methods of anti-histaminic treatment

4-[4-[4-(hydroxydiphenylmethyl)-1-piperidinyl]-1-hydroxybutyl]-α,α-dimethylbenzeneacetic acid of formula (I), fexofenadine, is an H₁ receptor antagonist and a useful antihistaminic drug

Various pharmaceutically acceptable salts of fexofenadine have been disclosed, for example EP 1178041A, page 5, paragraph 0010. EP 1178041A further describes the preparation of anhydrous fexofenadine hydrochloride (Forms I and III) and hydrated forms (Forms II and Form IV). The process described in EP 1178041A involves making the anhydrous Forms I and III from the hydrated Forms II and IV, for example by azeotropic distillation thus heating in acidic conditions for extended periods. Extended heating in this way can cause following impurities I and II to increase beyond acceptable levels

EP 1178041A also describes a water-limiting crystallization that involves crystallization of the hydrate, but this involves using large volumes of solvent so as to limit the water content of the solution to acceptable levels.

WO 01/94313 describes Form A of fexofenadine hydrochloride. The process for its preparation involves the use of water, which means Form A is prepared as a hydrated form, which is not suitable for pharmaceutical formulation.

U.S. Pat. No. 4,254,129 is the basic fexofenadine patent and describes fexofenadine HCl being isolated from aqueous hydrochloric acid, which will lead to the formation of a hydrated form, which as indicated above is not suitable for pharmaceutical formulation.

WO 93/21156 also relates to fexofenadine hydrochloride and Example 1 describes dissolving fexofenadine base in methylene dichloride and acidifying with HCl gas to pH 3. The reaction mass is then concentrated to residue, ether is added and the mixture is stirred to obtain solid, which is filtered to give fexofenadine hydrochloride. This process leads to the formation of amorphous fexofenadine hydrochloride, which has a tendency to pick up moisture and form lumps on storage, and as such is difficult to handle during formulation of tablets and capsules. Furthermore, the use of ether as described in the preparation thereof is not advisable on a commercial scale and hence the process described therein is unsuitable for industrial application.

Apart from the hydrochloride salt, in anhydrous and hydrated forms as discussed above, however, no other salt of fexofenadine has been exemplified in the prior art. Conversion of hydrated salts to their anhydrous forms by water minimizing crystallization is also claimed in EP 766668B, but the disclosure is limited to the inter-conversion of corresponding salts. The conversion of one salt, hydrated or otherwise, to a different anhydrous salt form is not reported or suggested.

The present invention now provides novel polymorphs of fexofenadine, whereby a first salt of fexofenadine in hydrated form can be converted directly to a different salt of fexofenadine in anhydrous form. More particularly, we have now found that fexofenadine acetate, and its hydrated forms, can be converted to a novel polymorph of anhydrous fexofenadine hydrochloride, which is distinguished from the fexofenadine hydrochloride polymorphs described in the prior art in respect of its melting point range, X-ray diffraction pattern and infra red absorption spectrum. Furthermore, advantages can be shown in respect of anhydrous fexofenadine hydrochloride according to the present invention compared to the prior art, for example the avoidance of associated impurities (such as impurities I and II described above) and also the free flowing nature thereof, which renders anhydrous fexofenadine hydrochloride according to the present invention particularly suitable for formulation use.

The present invention also provides fexofenadine free base monohydrate which can also be converted to the above novel polymorph of anhydrous fexofenadine hydrochloride.

More particularly, there is provided by the present invention anhydrous crystalline fexofenadine hydrochloride Form C.

The present invention also provides anhydrous crystalline fexofenadine hydrochloride Form C having an X-ray diffraction pattern, or substantially the same X-ray diffraction pattern, as shown in FIG. 1. More particularly, anhydrous crystalline fexofenadine hydrochloride Form C according to the present invention can be characterised as having an X-ray diffraction pattern with characteristic peaks (2θ): 8.9712°, 14.8293°, 16.0514°, 17.0775°, 18.3418°, 19.3099°, 19.7703°, 21.1340°, 21.5207°, 23.0743° and 23.8286°.

Further characterising data for anhydrous crystalline fexofenadine hydrochloride Form C according to the present invention as obtained by X-ray diffraction is shown in following table 1.

TABLE 1 2θ d Peak No. (deg) (A) I/II 1 6.0640 14.56317 5 2 8.5400 10.34563 4 3 8.9712 9.84931 30 4 9.4917 9.31033 6 5 12.2731 7.20591 8 6 14.2000 6.23213 7 7 14.8293 5.96904 100 8 15.3400 5.77145 9 9 16.0514 5.51723 30 10 16.3600 5.41384 8 11 17.0775 5.18796 31 12 17.4651 5.07369 10 13 18.3418 4.83311 25 14 19.3099 4.59293 22 15 19.7703 4.48700 38 16 21.1340 4.20045 22 17 21.5207 4.12584 15 18 22.1600 4.00823 3 19 22.5560 3.93875 6 20 23.0743 3.85144 22 21 23.8286 3.73120 17 22 25.3114 3.51588 17 23 25.8400 3.44514 8 24 26.0800 3.41398 12 25 26.6000 3.34841 3 26 26.9400 3.30691 4 27 27.2305 3.27229 8 28 27.9737 3.18702 4 29 28.8733 3.08974 14 30 29.6000 3.01551 5 31 29.9400 2.98204 9 32 31.3543 2.85068 9 33 31.6800 2.82211 3 34 34.7180 2.58180 3 35 35.6950 2.51334 3 36 37.5325 2.39441 3

Anhydrous crystalline fexofenadine hydrochloride Form C according to the present invention is preferably further characterised as having a melting point in the range of about 191 to 196° C. (DSC; open capsule). More specifically, anhydrous crystalline fexofenadine hydrochloride Form C according to the present invention is preferably further characterised as having a melting point in the range of about 192 to 194° C. (DSC; open capsule) as shown in FIG. 2, which is distinguished from the prior art polymorphs as discussed above.

Anhydrous cystalline fexofenadine hydrochloride Form C according to the present invention is preferably more than about 99.5% w/w pure (peak area).

Anhydrous crystalline fexofenadine hydrochloride Form C according to the present invention can also be further characterised as having an infra red absorption spectrum, or substantially the same infra red absorption spectrum, as shown in FIG. 3.

The term “anhydrous” as used herein with reference to crystalline fexofenadine hydrochloride Form C denotes a moisture content thereof of less than about 0.5% by weight

The present invention also provides hydrated crystalline fexofenadine acetate Forms D and E. Form D is crystalline fexofenadine acetate monohydrate. Form E is crystalline fexofenadine acetate dihydrate, which can be easily prepared on an industrial scale from fexofenadine free base substantially as hereinafter described in greater detail. Fexofenadine acetate dihydrate as provided by the present invention is crystalline, easy to filter and dry, and preparation of the acetate salt preferably removes most of the impurities that are otherwise difficult to remove.

Crystalline fexofenadine acetate dihydrate Form E according to the present invention can be characterised as having an infra red absorption spectrum, or substantially the same infra red absorption spectrum, as shown in FIG. 4.

The present invention also provides crystalline fexofenadine acetate dihydrate Form E having an X-ray diffraction pattern, or substantially the same X-ray diffraction pattern, as shown in FIG. 5. More particularly, crystalline fexofenadine acetate dihydrate Form E according to the present invention, can be characterised as having an X-ray diffraction pattern with characteristic peaks (2θ): 8.2266°, 9.3654°, 10.6929°, 11.1600°, 13.0400°, 13.4200°, 15.7473°, 16.4400°, 16.9785°, 17.5334°, 19.9728°, 20.7000°, 21.1236°, 23.0150° and 26.2977°.

Further characterising data for crystalline fexofenadine acetate dihydrate Form E according to the present invention as obtained by X-ray diffraction is shown in following table 2.

TABLE 2 2θ d Peak No. deg) (A) I/II 1 6.5665 13.44981 8 2 7.9000 11.18226 6 3 8.2266 10.73904 29 4 8.9200 9.90573 7 5 9.3654 9.43561 21 6 9.8798 8.94546 8 7 10.6929 8.26699 43 8 11.1600 7.92200 13 9 13.0400 6.78379 31 10 13.4200 6.59255 26 11 14.5800 6.07054 7 12 14.9000 5.94088 10 13 15.3800 5.75653 10 14 15.7473 5.62308 22 15 16.4400 5.38768 33 16 16.9785 5.21799 100 17 17.5334 5.05408 30 18 18.5000 4.79213 6 19 18.7200 4.73631 10 20 19.3200 4.59055 24 21 19.9728 4.44196 63 22 20.7000 4.20753 32 23 21.1236 4.20249 66 24 21.8975 4.05569 16 25 22.4623 3.95497 21 26 23.0150 3.86123 25 27 23.5600 3.77313 5 28 23.8600 3.72636 6 29 24.7800 3.59006 10 30 25.1800 3.53393 16 31 25.7600 3.45566 7 32 26.2977 3.38621 29 33 27.1413 3.28284 11 34 27.7071 3.21708 5 35 28.7490 3.10281 6 36 30.1035 2.96621 8 37 30.9400 2.88790 6 38 31.3454 2.85147 14

Crystalline fexofenadine acetate monohydrate Form E is further characterised by a typical DSC thermograph showing three endotherms, as shown in FIG. 6. Two endotherms, the first one between 74° C. to 87° C. and the second one between 130° to 143° C. signify loss of the water molecules, and a sharp endotherm having onset at about 216° C. is the melting endotherm. Crystalline fexofenadine acetate dihydrate Form E according to the present invention is preferably, therefore, further characterised as having a melting point in the range of about 216 to 229° C. (DSC; open capsule) and DSC characteristics as shown in FIG. 6.

Crystalline fexofenadine acetate dihydrate Form E according to the present invention is preferably more than about 99.5% w/w pure (peak area).

The term “monohydrate” as used herein with reference to crystalline fexofenadine acetate Form D denotes a moisture content thereof in the range of about 3 to 5% by weight The term “dihydrate” as used herein with reference to crystalline fexofenadine acetate Form E denotes a moisture content thereof in the range of about 6 to 8% by weight.

The present invention also provides crystalline fexofenadine free base monohydrate Form F.

Crystalline fexofenadine free base monohydrate Form F according to the present invention can be characterised as having an infra red absorption spectrum, or substantially the same infra red absorption spectrum, as shown in FIG. 7.

The present invention also provides crystalline fexofenadine free base monohydrate Form F having an X-ray diffraction pattern, or substantially the same X-ray diffraction pattern, as shown in FIG. 8. More particularly, crystalline fexofenadine free base monohydrate Form F according to the present invention, can be characterised as having an X-ray diffraction pattern with characteristic peaks (2θ): 3.6184°, 7.2914°, 9.5669°, 11.4946°, 11.9468°, 17,8400°, 18.2536°, 19.4768°, 21.6636°, 23.7517° and 25.6771°.

Further characterising data for crystalline fexofenadine free base monohydrate Form F according to the present invention as obtained by X-ray diffraction is shown in following table 3.

TABLE 3 2θ d Peak No. (deg) (A) I/II 1 3.6184 24.39878 53 2 7.2914 12.11420 12 3 9.5669 9.23732 22 4 11.4946 7.69214 26 5 11.9468 7.40198 13 6 13.2800 6.66173 7 7 13.6800 6.46783 16 8 14.0800 6.28497 9 9 16.0591 5.51460 11 10 17.8400 4.96791 76 11 18.2536 4.85626 100 12 19.4768 4.55395 53 13 20.5000 4.32890 21 14 20.8600 4.25500 20 15 21.3800 4.15267 16 16 21.6636 4.09894 34 17 22.5525 3.93935 18 18 23.7517 3.74310 23 19 25.6771 3.46663 22 20 26.5400 3.35584 16 21 26.8600 3.31658 15 22 27.7305 3.21441 10 23 28.5977 3.11888 12 24 30.2654 2.95071 10 25 31.1246 2.87119 14 26 32.3453 2.76556 10 27 35.8600 2.50215 7

Fexofenadine base monohydrate Form F is further characterised by a typical DSC thermograph showing two endotherms, as shown in FIG. 9. A broad endotherm between 70° C. to 102° C. signifies loss of the water molecule, and a sharp endotherm having onset at about 222° C. the melting endotherm There are two minor exotherms (between the two endotherms) likely to be indicative of phase transitions at high temperatures. Fexofenadine base monohydrate Form F according to the present invention is preferably, therefore, further characterised as having a melting point in the range of about 222 to 231° C. (DSC; open capsule) and DSC characteristics as shown in FIG. 9.

Crystalline fexofenadine free base monohydrate Form F according to the present invention is preferably more than about 99.5% w/w pure (peak area).

Fexofenadine has therapeutic utility as an H₁ receptor antagonist and is useful for administration to a patient to alleviate symptoms caused by histamine. As an antihistamine, fexofenadine is effective at relieving symptoms caused by airborne and contact inducers of histamine release. Such substances include pollen, spores, animal dander, industrial chemicals, dust and dust mites. Symptoms that can be alleviated by fexofenadine include bronchial spasms, sneezing, rhinorrhia, nasal congestion, lacrimation, redness, rash, urticaria and itch The wording “anti-histaminic treatment” as used herein covers treatment of any of the above symptoms.

Fexofenadine polymorphs C, D, E or F, especially anhydrous crystalline fexofenadine hydrochloride Form C, as provided by the present invention, are useful for delivering fexofenadine to the gastrointestinal tract, mucus membranes, bloodstream and inflamed tissues of a patient suffering from inflammation caused by histamine. Fexofenadine Forms C, D, E or F, especially anhydrous crystalline fexofenadine hydrochloride Form C, are suitable for inclusion in pharmaceutical compositions for use in antihistaminic treatment and are also suitable for use in methods of treating a patient suffering from or susceptible to inflammation caused by histamine.

The present invention further provides, therefore, a pharmaceutically acceptable composition for antihistaminic treatment, which composition comprises a therapeutically effective amount of any of fexofenadine Forms C, D, E or F as described herein, especially anhydrous crystalline fexofenadine hydrochloride Form C, together with a pharmaceutically acceptable carrier, diluent or excipient therefor.

As used herein, the term “therapeutically effective amount” means an amount of any of fexofenadine Forms C, D, E or F which is capable of preventing, ameliorating or eliminating inflammation caused by histamine.

By “pharmaceutically acceptable composition” it is meant that the carrier, diluent or excipient is compatible with any of fexofenadine Forms C, D, E or F and not deleterious to a recipient thereof. Fexofenadine Forms C, D, E or F according to the present invention have been found to be suitable for formulation into stable solid compositions exhibiting good release properties.

The pharmaceutical compositions of the present invention may be administered in any suitable way and in any suitable form, for example orally (preferred) in the form of tablets, capsules, powders or liquid compositions (for example syrups), or for example parenterally in the form of conventional sterile solutions for injection, or inhalant or ophthalmic compositions.

The pharmaceutical compositions of the present invention may be prepared by conventional methods known in the art. For example, tablets may be prepared by mixing any of fexofenadine Forms C, D, E or F according to the present invention, with known adjuvants and/or diluents and subsequently compressing the mixture in a conventional tabletting machine. Examples of adjuvants or diluents can comprise corn starch, potato starch, talcum, magnesium stearate, gelatine, lactose, gums, and the like. Other adjuvants or additives such as colourings, aroma enhancers, preservatives and the like may be used provided that they are compatible with fexofenadine Forms C, D, E or F as described herein.

In liquid pharmaceutical compositions as provided by the present invention, any of fexofenadine Forms C, D, E or F, and any other solid excipients, can be dissolved or suspended in a liquid carrier such as water, vegetable oil, alcohol, polyethylene glycol, propylene glycol or glycerin Liquid pharmaceutical compositions according to the present invention can where required also further comprise emulsifying agents, viscosity enhancing agents, sweetening agents, preservatives and buffers.

The particular dosage form of fexofenadine Forms C, D, E or F, especially anhydrous crystalline fexofenadine hydrochloride Form C, required for antihistaminic treatment as provided by the present invention will depend on the particular inflammation caused by histamine, and the symptoms and severity thereof. Dosage, routes of administration, and frequency of dosing are best decided by an attending physician.

The present invention further provides fexofenadine Forms C, D, E or F for use in the manufacture of a medicament for antihistaminic treatment.

The present invention also provides a method of antihistaminic treatment, which method comprises administering to a patient a therapeutically effective amount of any of fexofenadine Forms C, D, E or F, especially anhydrous crystalline fexofenadine hydrochloride Form C.

A further aspect of the present invention is a novel process for preparation of fexofenadine free base as a monohydrate by hydrolysis of a keto ester of formula III to the corresponding keto acid of formula II and subsequent reduction of the acid, suitably with sodium borohydride under aqueous or alcoholic conditions to give sodium salt of fexofenadine which is converted to the free base by pH adjustment

There is provided by the present invention, therefore, a process of preparing fexofenadine, which process comprises reduction of a compound of formula (II)

and isolation of fexofenadine free base monohydrate in crystalline form. Suitable reducing agents can include sodium borohydride, sodium cyanoborohydride, lithium aluminum hydride or the like. Preferably sodium borohydride is employed, and a compound of formula (II) can be reduced to initially yield the sodium salt of fexofenadine as indicated above, which is then converted to the free base by pH adjustment

A process according to the present invention can further comprises, preparation of a compound of formula (II) by hydrolysis of a compound of formula (III)

where R₁ is a suitable carboxy protecting group, such as C₁-C₄alkyl, in particular methyl.

The present invention further comprises a process of preparing fexofenadine, which process comprises hydrolysis of a compound of formula (III)

to yield a compound of formula (II)

followed by reduction of a compound of formula (II) and isolation of fexofenadine free base monohydrate in crystalline form, and optionally converting said fexofenadine free base to a pharmaceutically acceptable salt.

In a process according to the present invention, it is preferred that a compound of formula (III) is prepared by the reaction of a protected derivative of formula (IV)

where Hal is chloro, bromo or iodo, in particular chloro, and R₁ is a suitable carboxy protecting group, such as C₁-C₄alkyl, in particular methyl, as referred to above, with azacyclonal of formula (V)

Typically a compound of formula (IV) is prepared from a protected derivative of formula (VI)

where Hal is as defined above and R₂ is a suitable hydroxy protecting group, such as acetyl or benzyl, preferably acetyl, by a series of steps comprising deprotection, oxidation and subsequent re-protection prior to reaction with a compound of formula (V). Typically the reaction sequence can be represented as follows

A compound of formula (VI) is typically prepared by reaction of a protected derivative of formula (IX)

where R₂ is a suitable hydroxy protecting group, such as acetyl or benzyl, preferably acetyl, as referred to above, with a halo compound of formula (X)

where Hal is as defined above and B is halo or hydroxy, typically halo and in particular chloro, suitably under the general conditions of a Friedel-Crafts acylation in the presence of a suitable Lewis acid. Suitable Lewis acids are well known in the art and include boron trichloride, aluminum chloride, titanium tetrachloride, boron trifluoride, tin tetrachloride, ferric chloride, cobalt (II) chloride and zinc chloride, with aluminum chloride being preferred.

A compound of formula (IX) is suitably prepared by protection of the corresponding hydroxy compound of formula (XI)

by introduction of protecting group R₂, suitably by esterification.

A compound of formula (XI) is suitably prepared by esterification of a compound of formula (XII) and subsequent reduction of a compound of formula (XIII) according to the following reaction sequence

where R₃ is C₁-C₄alkyl, in particular methyl.

Suitably, a compound of formula (XII) is prepared by methylation of a compound of formula (XIV) and subsequent hydrolysis of a compound of formula (XV) according to the following reaction sequence

The above reaction steps typically yield fexofenadine free base monohydrate, which preferably can be further converted into a pharmaceutically acceptable salt Suitable salts can include acetate and hydrochloride salts substantially as hereinbefore described and as represented by any of fexofenadine Forms C, D or E as provided by the present invention. Preferably a process substantially as hereinbefore described, therefore, further comprises treating fexofenadine free base, typically fexofenadine free base monohydrate Form F, with a pharmaceutically acceptable acid so as to yield a pharmaceutically acceptable salt, in particular treatment with hydrochloride acid and/or acetic acid to prepare any of anhydrous crystalline fexofenadine hydrochloride Form C, crystalline fexofenadine acetate monohydrate Form D or crystalline fexofenadine acetate dihydrate Form E as provided by the present invention.

In a particular embodiment, a process substantially as hereinbefore described further comprises reaction of fexofenadine free base monohydrate Form F as prepared thereby with hydrochloride acid so as to yield anhydrous crystalline fexofenadine hydrochloride Form C.

In an alternative embodiment, a process substantially as hereinbefore described further comprises reaction of fexofenadine free base monohydrate Form F as prepared thereby with acetic acid to yield crystalline fexofenadine acetate monohydrate Form D and subsequent conversion thereof (typically by exposing fexofenadine acetate monohydrate Form D to an atmosphere of sufficient humidity and for a sufficient amount of time) to crystalline fexofenadine acetate dihydrate Form E. Crystalline fexofenadine acetate dihydrate Form E can then be treated with hydrochloride acid so as to yield anhydrous crystalline fexofenadine hydrochloride Form C.

In a still further alternative embodiment, a process substantially as hereinbefore described further comprises reaction of fexofenadine free base monohydrate as prepared thereby with acetic acid to yield crystalline fexofenadine acetate dihydrate Form E. Crystalline fexofenadine acetate dihydrate Form E can then be treated with hydrochloride acid so as to yield anhydrous crystalline fexofenadine hydrochloride Form C.

According to the present invention there is further provided a process of preparing crystalline fexofenadine acetate monohydrate Form D from crystalline fexofenadine free base monohydrate Form F. Typically, this process comprises dissolving crystalline fexofenadine free base monohydrate Form F in a first aqueous solution (such as aqueous sodium hydroxide) and converting the free carboxyl group of fexofenadine to an alkali metal salt functionality (such as the sodium salt), quenching the resulting aqueous solution into a further aqueous solution containing an excess of acetic acid and effecting precipitation of crystalline fexofenadine acetate monohydrate Form D therefrom.

According to the present invention, there is still further provided a process of preparing crystalline fexofenadine acetate dihydrate Form E from crystalline fexofenadine acetate monohydrate Form D, which comprises exposing fexofenadine acetate monohydrate Form D to an atmosphere of sufficient humidity and for a sufficient amount of time to yield crystalline fexofenadine acetate dihydrate Form E.

According to the present invention there is further provided a process of preparing crystalline fexofenadine acetate dihydrate Form E from crystalline fexofenadine free base monohydrate Form F. Typically, this process comprises dissolving crystalline fexofenadine free base monohydrate Form F in a first aqueous solution (such as aqueous sodium hydroxide) and converting the free carboxyl group of fexofenadine to an alkali metal salt functionality (such as the sodium salt), quenching the resulting aqueous solution into a further aqueous solution containing an excess of acetic acid and effecting precipitation of crystalline fexofenadine acetate dihydrate Form E therefrom

According to the present invention there is further provided a process of preparing anhydrous crystalline fexofenadine hydrochloride Form C from crystalline fexofenadine free base monohydrate Form F. Typically this process comprises reaction of crystalline fexofenadine free base monohydrate Form F with hydrochloride acid. Preferably, crystalline fexofenadine free base monohydrate Form F is suspended in a first organic solvent medium and hydrochloric acid (typically as dry hydrochloric acid gas) is added thereto; concentrating to obtain a residue; adding the residue to a second organic solvent medium and effecting precipitation of anhydrous crystalline fexofenadine hydrochloride Form C therefrom

Typically, the first organic solvent medium can comprise a ketone as the solvent, such as acetone; alternatively the first organic solvent medium can comprise THF. Typically, the second organic solvent medium can comprise a mixture of an ester and an alcohol, such as isopropanol and ethyl acetate.

According to the present invention there is further provided a process of preparing anhydrous crystalline fexofenadine hydrochloride Form C from crystalline fexofenadine acetate dihydrate Form E, wherein crystalline fexofenadine acetate dihydrate Form E is prepared from crystalline fexofenadine free base monohydrate Form F. Crystalline fexofenadine acetate dihydrate Form E can be prepared directly from crystalline fexofenadine free base monohydrate Form F, or via crystalline fexofenadine acetate monohydrate Form D substantially as hereinbefore described. Typically this process comprises reaction of crystalline fexofenadine acetate dihydrate Form E with hydrochloride acid. Preferably, crystalline fexofenadine acetate dihydrate Form E is suspended in a first organic solvent medium and hydrochloric acid (typically as dry hydrochloric acid gas) is added thereto; concentrating to obtain a residue; adding the residue to a second organic solvent medium and effecting precipitation of anhydrous crystalline fexofenadine hydrochloride Form C therefrom. Typically, the first organic solvent medium can comprise a ketone as the solvent, such as acetone; alternatively the first organic solvent medium can comprise THF. Typically, the second organic solvent medium can comprise a mixture of an ester and an alcohol, such as isopropanol and ethyl acetate.

In each of the above processes for the preparation of anhydrous crystalline fexofenadine hydrochloride Form C, this is prepared from either crystalline fexofenadine free base monohydrate Form F or crystalline fexofenadine acetate dihydrate Form E, without going through hydrated fexofenadine hydrochloride.

The present invention further provides use of crystalline fexofenadine free base monohydrate Form F substantially as hereinbefore described, for preparation of anhydrous fexofenadine hydrochloride (any form). There is also provided by the present invention use of crystalline fexofenadine acetate dihydrate Form E substantially as hereinbefore described, for preparation of anhydrous fexofenadine hydrochloride (any form).

There is further provided by the present invention any of anhydrous crystalline fexofenadine hydrochloride Form C, crystalline fexofenadine acetate monohydrate Form D, crystalline fexofenadine acetate dihydrate Form E and crystalline fexofenadine free base monohydrate Form F, prepared by a process substantially as hereinbefore described.

The present invention will now be further illustrated by the following Figures, Intermediates and Examples, which do not limit the scope of the invention in any way. In the experimental of the following Intermediates, where reactants or reagents are described as “above”, this means they are employed in the amounts specified therefor in the foregoing lists of reactants and reagents.

FIG. 1 is a PXRD pattern of anhydrous fexofenadine hydrochloride.

FIG. 2 is a DSC pattern of anhydrous fexofenadine hydrochloride.

FIG. 3 is an IR spectrum of anhydrous fexofenadine hydrochloride.

FIG. 4 is an IR spectrum of fexofenadine acetate dihydrate.

FIG. 5 is a PXRD pattern of fexofenadine acetate dihydrate.

FIG. 6 is a DSC pattern of fexofenadine acetate dihydrate.

FIG. 7 is an IR spectrum of fexofenadine base monohydrate.

FIG. 8 is a PXRD pattern of fexofenadine base monohydrate.

FIG. 9 is a DSC pattern of fexofenadine base monohydrate.

INTERMEDIATES Intermediate 1 Preparation of 2,2-dimethyl-2-phenyl-acetic acid

Benzyl cyanide (0.5 kg), potassium hydroxide (1.4 kg) and DMSO (2.5 ltr) were initially charged to a reactor and dimethyl sulphate (1.20 kg) was slowly added thereto over a period of one hour. The mixture was stirred for 3-4 hours at room temperature. The mass was slowly quenched in water with stirring. The pH was adjusted to 1-2 with conc HCl. The solution was filtered, the solids washed with water and the resulting material was dried under vacuum in an oven. The resulting product was suspended in water (3.0 ltr), sodium hydroxide (0.5 kg) added thereto and the mixture refluxed for 6 hours. After completion of the reaction, the reaction mass was cooled to room temperature and acidified with HCl to pH 2-3. The resulting precipitated material was filtered, washed with water and dried to obtain the title product.

Intermediate 2 Preparation of methyl-2,2-dimethyl-2-phenyl acetate

Methanol (2.5 ltr), 2,2-dimethyl-2-phenyl-acetic acid (Intermediate 1) (0.5 kg), and conc. sulphuric acid (50 ml) were charged to a reactor at room temperature. The temperature was raised to reflux and maintained for 12 hours. The pH was adjusted to 7-8 using aqueous ammonia and the methanol concentrated completely. The reaction mass was quenched in water (1 ltr) and extracted with MDC (750 ml). The MDC layer was dried over sodium sulphate and concentrated to obtain 500 gms of the title compound as an oil having 98% purity.

Intermediate 3 Preparation of 2-methyl-2-phenyl-propanol

Methyl-2,2-dimethyl-2-phenyl acetate (Intermediate 2) (0.5 kg), and THF (2.5 ltr) were charged to a reactor, and sodium borohydride (100 gms) was added in lots. The mixture was stirred at room temperature for 5 hours. After completion of the reaction, the pH was adjusted to 3-4 with HCl, the inorganics filtered and the filtrate concentrated and stripped with toluene (50 ml) to obtain the title compound as an oil weighing 400 gms.

Intermediate 4 Preparation of methyl 2-methyl-2-phenyl-propanoate

2-methyl-2-phenyl-propanol (Intermediate 3) (0.5 kg) and pyridine (268 ml) were charged to a reactor and chilled to 0° C. Acetic anhydride (680 gms) was slowly added through a dropper at 10-20° C. The mixture was stirred for 2 hours at 10-20° C. Ethyl acetate (1.5 ltr) was added and chilled water (2 ltrs) was slowly added through a dropper at 10-20° C. The mixture was stirred for ½ hr. The ethyl acetate layer was separated and 10% chilled dilute HCl was added. The ethyl acetate layer was then washed with sodium bicarbonate until a pH of 7 was obtained. The ethyl acetate layer was dried with sodium sulphate and concentrated under vacuum The resulting oil was distilled under vacuum (15 mm of Hg). at 80-100° C.

Intermediate 5 Preparation of methyl-2-[4-(4-chloro-butyryl-)phenyl]-2-methyl-propanoate

MDC (600 ml) and aluminum chloride (347 gms) were charged to a reactor and chilled to −10° C. Methyl-2-methyl-2 phenyl-propanoate (Intermediate 4) (500 gms) was dissolved in MDC (650 ml) and added slowly through a dropper at −10 to 0° C. to obtain mixture A. MDC (600 ml) and aluminum chloride (520 gms) were charged to a different reactor, and chilled to −10° C. 4-chloro butyryl chloride (550 gms) was dissolved in MDC (650 ml) and added slowly through a dropper at −10 to 0° C. to obtain mixture B. Both mixtures A and B were stirred for 45 minutes at −10 to 0° C. separately. Mixture A was added to mixture B slowly at −10 to 0° C. and the reaction monitored by GC for completion (24 hours). The mass was quenched slowly in conc. HCl (1 ltr) at 10-20° C. and stirred for 30 minutes. The MDC layer was separated and the aqueous layer extracted with MDC (500 ml). The combined MDC layer was dried over sodium sulfate and concentrated under vacuum to obtain 880 gms of the title compound as an oil.

Intermediate 6 Preparation of 2-[4-(4-chloro-butyryl)phenyl]-2-methyl-propanol

Methyl-2-[4-(4-chlorobutyryl)-phenyl]-2-methyl propanoate (Intermediate 5) (0.5 kg) and methanol (750 ml) were charged to a reactor and cooled to 10-20° C. Conc. HCl (250 ml) was added at 10-20° C. and stirred for 24 hours at room temperature. The reaction was monitored by TLC for completion. The pH of the reaction mass was adjusted to 7-8 with aqueous ammonia at 20-30° C. and the methanol was concentrated. The reaction mixture was quenched in water (1 ltr) and extracted with MDC (500 ml). The MDC layer was dried over sodium sulphate and concentrated to obtain 400 gms of the title compound as an oil.

Intermediate 7 Preparation of 2-[4-(4-chloro-butyryl-phenyl]-2-methyl-propanoic acid

Acetic acid (1.0 ltr) and acetone (1.0 ltr) were charged to a reactor. Potassium permanganate (464 gms) was charged to the reactor and the mass chilled to 0° C. 2-[4-(4-chlorobutyrl)phenyl])-2-methyl propanol (Intermediate 6) (0.5 kg) was dissolved in acetone (500 ml) and added slowly at 0° C.-10° C. The reaction mass was stirred at 10-20° C. for 15 hours. MDC (1 ltr) was added to the reaction mass. Sodium metabisulphite (250 gms) was dissolved in water (1½ ltr) and added to the reaction mass at 10-20° C. The colour of the reaction mass changed from brown to colourless. The MDC layer was separated and the aqueous layer was extracted with MDC (250 ml). The MDC layer was separated. The MDC layers were combined and dried over sodium sulphate. The MDC layer was concentrated to obtain 575 gms of crude oil. Potassium carbonate (232 gms) was dissolved in water (1 ltr) and added to the oil. The pH was 9-10. Ethyl acetate was chilled to 10° C. and 6 extractions (each 300 ml) of the aqueous layer were carried out with the chilled ethyl acetate. MDC (750 ml) was added to the aqueous solution. The pH of the aqueous layer was adjusted to 5 using dilute HCl in biphase. The MDC layer was separated and MDC (250 ml) was again employed to extract the aqueous layer. The MDC layer was separated. The MDC layers were combined and dried over sodium sulphate. The MDC was concentrated to obtain the title compound as an oil weighing 265 gms.

Intermediate 8 Preparation of methyl 2-[4-(4-chloro-butyryl)phenyl)]-2-methyl-propionate

Acetone (3.5 ltr), 2-[4-(4-chlorobutyryl)phenyl]-2 methyl propanoic acid (Intermediate 7) (0.5 kg) and anhydrous potassium carbonate (232 gms) were charged to a reactor and chilled to 10° C. Dimethyl sulphate (234 gms) was slowly added at 10-20° C. and the reaction mixture stirred at room temperature for 5 hours. The mixture was heated to 35-40° C. for 2 hours until the reaction was complete. The reaction mass was filtered and the acetone concentrated. MDC (600 ml) was added, the MDC layer separated and washed with water. The MDC layer was dried over sodium sulphate and the MDC concentrated to obtain the title compound as a light brown oil weighing 460 gms.

Intermediate 9 Preparation of 4-[4-(4-hydroxy diphenyl methyl)-1-piperidinyl]-1-oxybutyl]-α, α-dimethyl benzene acetic, methyl ester

Methyl-2-[4-(4-chloro-1-oxo-butyl]phenyl]-2-methyl propionate (Intermediate 8) (0.5 kg), anhydrous potassium carbonate (349 gms), potassium iodide (9.7 gms), azacyclonol (328 gms), MIBK (2.0 ltr) and DMF (0.5 ltr) were charged to a reactor. A Dean and Stark arrangement for water removal was set up (about 10 ml of water separated out). The reaction mass was heated for 18 hours at 120° C. The reaction mass was then cooled to room temperature and the inorganics filtered. The MIBK layer was then washed with water. The MIBK was concentrated to obtain 800 gms of oil. 2 volumes of alcohol were charged and stirred at 40° C. for 2 hours, followed by cooling to 5° C. The solids were filtered and dried to obtain the title compound.

EXAMPLES Example 1 Preparation of fexofenadine Free Base monohydrate

4-[4-(4-hydroxydiphenyl methyl)-1-piperidinyl]-1-oxo-butyl]-α,α-dimethyl benzene acetic, methyl ester (20 gms) (Intermediate 9) was suspended in isopropanol (75 ml) and 25% sodium hydroxide solution (4 ml) was added. The mixture was refluxed for 5 hours. The pH of the reaction mixture was adjusted to 5.5-6 with dilute acetic acid. The precipitated product was filtered and dried to give 4-[4-(4-hydroxydiphenyl methyl)-1-piperidinyl]-1-oxo-butyl]-α,α-dimethyl benzene acetic acid.

The above product was suspended in methanol and sodium borohydride (0.75 gms) was added slowly over 2 hours. The mixture was stirred at 30° C. for 10 hours. The pH of the mixture was adjusted to 5.5 to 6 with dilute acetic acid. The precipitated product was filtered and dried to give fexofenadine base monohydrate.

Example 2 Preparation of fexofenadine acetate monohydratye

Fexofenadine base was suspended in a 5% aqueous sodium hydroxide solution (250 ml). The mixture was stirred to get a clear solution The clear solution was then quenched at room temperature into a mixture of acetic acid (35 gms) in water (250 ml). The mixture was stirred for 1 hour at room temperature and the solids filtered and washed with water to obtain a neutral pH. The solids were dried under vacuum at 60°-70° C. until the moisture content was between 3.5% to 4.2%.

Example 3 Preparation of fexofenadine acetate dihydrate

Fexofenadine base was suspended in a 5% aqueous sodium hydroxide solution (250 ml). The mixture was stirred to get a clear solution. The clear solution was then quenched at room temperature into a mixture of acetic acid (35 gms) in water (250 ml). The mixture was stirred for 1 hour at room temperature and the solids filtered and washed with water to obtain a neutral pH. The solids were dried under vacuum at 60°-70° C. until the moisture content was between 6.5% to 7.7%.

Example 4 Preparation of fexofenadine acetate dihydrate

Fexofenadine acetate monohydrate was exposed to an atmosphere of 60% relative humidity for 4 hours at 30° C. to give fexofenadine acetate dihydrate having a moisture content of 6.9-7.5%.

Example 5 Preparation of anhydrous fexofenadine hydrochloride

(i) Process from Fexofenadine acetate

Fexofenadine acetate (25 gms) was suspended in acetone (100 ml). Dry hydrochloric acid gas was bubbled into the suspension maintaining the temperature in the range of 25° C. to 30° C. The pH of the mixture was adjusted to between 1-2 to get a clear solution The clear acetone solution was concentrated under vacuum to get a residue. The residue was stripped with acetone followed by toluene to remove traces of hydrogen chloride.

To the residue was added 250 ml of a mixture of isopropanol and ethyl acetate (1:9) and stirred at about 25° C. for 3-4 hours until the precipitation was complete. The reaction mixture was cooled to 5° C., the solids filtered. The product was dried under vacuum at 60° C.-70° C. until the moisture content was less than 0.5%.

(ii) Process from Fexofenadine Base

Fexofenadine base (25 gms) was suspended in acetone (100 ml). Dry hydrochloric acid gas was bubbled into the suspension maintaining the temperature in the range of 25° C. to 30° C. The pH of the mixture was adjusted to between 1-2 to get a clear solution. The clear acetone solution was concentrated under vacuum to get a residue. The residue was stripped with acetone followed by toluene to remove traces of hydrogen chloride.

To the residue was added 250 ml of a mixture of isopropanol and ethyl acetate (1:9) and stirred at about 25° C. for 3-4 hours until the precipitation was complete. The reaction mixture was cooled to 5° C., the solids filtered. The product was dried under vacuum at 60° C.-70° C. until the moisture content was less than 0.5%.

(iii) Process from Fexofenadine acetate

Fexofenadine acetate (25 gms) was suspended in tetrahydrofuran (75 ml). Dry hydrochloric acid gas was bubbled into the suspension maintaining the temperature in the range of 25° C. to 30° C. The pH of the mixture was adjusted between 1-2 to get a clear solution. The clear THF solution was concentrated under vacuum to get a residue. The residue was stripped with THF followed by toluene to remove traces of hydrogen chloride.

To the residue was added 250 ml of a mixture of isopropanol and ethyl acetate (1:9) and stirred at about 25° C. for 3-4 hours until the precipitation was complete. The reaction mixture was cooled to 5° C., the solids filtered. The product was dried under vacuum at 60° C.-70° C. until the moisture content was less than 0.5%.

(iv) Process from Fexofenadine Base

Fexofenadine base (25 gms) was suspended in tetrahydrofuran (70 ml). Dry hydrochloric acid gas was bubbled into the suspension maintaining the temperature in the range of 25° C. to 30° C. The pH of the mixture was adjusted to between 1-2 to get a clear solution The clear THF solution was concentrated under vacuum to get a residue. The residue was stripped with THF followed by toluene to remove traces of hydrogen chloride.

To the residue was added 250 ml of a mixture of isopropanol and ethyl acetate (1:9) and stirred at about 25° C. for 3-4 hours until the precipitation was complete. The reaction mixture was cooled to 5° C., the solids filtered. The product was dried under vacuum at 60° C.-70° C. until the moisture content was less than 0.5%. 

1. Anhydrous crystalline fexofenadine hydrochloride Form C having an X-ray diffraction pattern as shown in FIG.
 1. 2. Anhydrous crystalline fexofenadine hydrochloride Form C characterised as having an X-ray diffraction pattern with characteristic peaks (2θ): 8.9712°, 14.8293°, 16.0514°, 17.0775°, 18.3418°, 19.3099°, 19.7703°, 21.1340°, 21.5207°, 23.0743° and 23.8286°.
 3. Anhydrous crystalline fexofenadine hydrochloride Form C according to claim 1 characterised as having a melting point in the range of about 192 to 194° C.
 4. Anhydrous crystalline fexofenadine hydrochloride Form C according to claim 1 characterised as having an infra red absorption spectrum as shown in FIG.
 3. 5. Fexofenadine hydrochloride Form C according to claim 1, which is more than about 99.5% w/w pure.
 6. Fexofenadine hydrochloride Form C according to claim 1, which is characterised by a moisture content thereof of less than about 0.5% by weight.
 7. A process of preparing anhydrous crystalline fexofenadine hydrochloride Form C from crystalline fexofenadine free base monohydrate Form F comprising suspending crystalline fexofenadine free base monohydrate Form F in a first organic solvent medium and adding hydrochloric acid thereto; concentrating to obtain a residue; adding the residue to a second organic solvent medium and effecting precipitation of anhydrous crystalline fexofenadine hydrochloride Form C therefrom, wherein anhydrous crystalline fexofenadine hydrochloride Form C has an X-ray diffraction pattern as shown in FIG.
 1. 8. A process of preparing anhydrous crystalline fexofenadine hydrochloride Form C from crystalline fexofenadine acetate dihydrate Form B comprising suspending crystalline fexofenadine acetate dihydrate Form B in a first organic solvent medium and adding hydrochloric acid thereto; concentrating to obtain a residue; adding the residue to a second organic solvent medium and effecting precipitation of anhydrous crystalline fexofenadine hydrochloride Form C therefrom, wherein anhydrous crystalline fexofenadine hydrochloride Form C has an X-ray diffraction pattern as shown in FIG.
 1. 9. A process of preparing fexofenadine, which process comprises reduction of a compound of formula (II)

and isolation of fexofenadine free base monohydrate in crystalline form, which further comprises converting fexofenadine free base monohydrate Form F obtained thereby to a pharmaceutically acceptable salt, which comprises converting crystalline fexofenadine free base monohydrate Form F to anhydrous crystalline fexofenadine hydrochloride Form C, wherein anhydrous crystalline fexofenadine hydrochloride Form C has an X-ray diffraction pattern as shown in FIG.
 1. 10. Anhydrous crystalline fexofenadine hydrochloride Form C according to claim 2 characterised as having a melting point in the range of about 192 to 194° C.
 11. Anhydrous crystalline fexofenadine hydrochloride Form C according to claim 2 characterised as having an infra red absorption spectrum as shown in FIG.
 3. 12. Fexofenadine hydrochloride Form C according to claim 2, which is more than about 99.5% w/w pure.
 13. Fexofenadine hydrochloride Form C according to claim 2, which is characterised by a moisture content thereof of less than about 0.5% by weight.
 14. A process of preparing anhydrous crystalline fexofenadine hydrochloride Form C from crystalline fexofenadine free base monohydrate Form F comprising suspending crystalline fexofenadine free base monohydrate Form F in a first organic solvent medium and adding hydrochloric acid thereto; concentrating to obtain a residue; adding the residue to a second organic solvent medium and effecting precipitation of anhydrous crystalline fexofenadine hydrochloride Form C therefrom, wherein anhydrous crystalline fexofenadine hydrochloride Form C is characterised as having an X-ray diffraction pattern with characteristic peaks (2θ): 8.9712°, 14.8293°, 16.0514°, 17.0775°, 18.3418°, 19.3099°, 19.7703°, 21.1340°, 21.5207°, 23.0743° and 23.8286°.
 15. A process of preparing anhydrous crystalline fexofenadine hydrochloride Form C from crystalline fexofenadine acetate dihydrate Form B comprising suspending crystalline fexofenadine acetate dihydrate Form B in a first organic solvent medium and adding hydrochloric acid thereto; concentrating to obtain a residue; adding the residue to a second organic solvent medium and effecting precipitation of anhydrous crystalline fexofenadine hydrochloride Form C therefrom, wherein anhydrous crystalline fexofenadine hydrochloride Form C is characterised as having an X-ray diffraction pattern with characteristic peaks (2θ): 8.9712°, 14.8293°, 16.0514°, 17.0775°, 18.3418°, 19.3099°, 19.7703°, 21.1340°, 21.5207°, 23.0743° and 23.8286°.
 16. A process of preparing fexofenadine, which process comprises reduction of a compound of formula (II)

and isolation of fexofenadine free base monohydrate in crystalline form, which further comprises converting fexofenadine free base monohydrate Form F obtained thereby to a pharmaceutically acceptable salt, which comprises converting crystalline fexofenadine free base monohydrate Form F to anhydrous crystalline fexofenadine hydrochloride Form C, wherein anhydrous crystalline fexofenadine hydrochloride Form C is characterised as having an X-ray diffraction pattern with characteristic peaks (2θ): 8.97 12°, 14.8293°, 16.0514°, 17.0775°, 18.3418°, 19.3099°, 19.7703°, 21.1340°, 21.5207°, 23.0743° and 23.8286°. 